<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>粒子背景</title>
    <style>
      html {
        height: 100%;
      }
      body {
        margin: 0;
        height: 100%;
        background: #fff;
      }
      canvas {
        display: block;
        width: 100%;
        height: 100%;
      }
      .text {
        width: 100%;
        background: transparent;
        display: flex;
        justify-content: center;
        height: 100%;
        line-height: 100%;
        top: 0;
        position: absolute;
        top: 50%;
        font-size: 50px;
      }
    </style>
  </head>
  <body>
    <canvas id="canvas"></canvas>
    <script>
      class Circle {
        //创建对象
        //以一个圆为对象
        //设置随机的 x，y坐标，r半径，_mx，_my移动的距离
        //this.r是创建圆的半径，参数越大半径越大
        //this._mx,this._my是移动的距离，参数越大移动
        constructor(x, y) {
          this.x = x;
          this.y = y;
          this.r = Math.random() * 10;
          this._mx = Math.random();
          this._my = Math.random();
        }

        //canvas 画圆和画直线
        //画圆就是正常的用canvas画一个圆
        //画直线是两个圆连线，为了避免直线过多，给圆圈距离设置了一个值，距离很远的圆圈，就不做连线处理
        drawCircle(ctx) {
          ctx.beginPath();
          //arc() 方法使用一个中心点和半径，为一个画布的当前子路径添加一条弧。
          ctx.arc(this.x, this.y, this.r, 0, 360);
          ctx.closePath();
          ctx.fillStyle = "rgba(204, 204, 204, 0.3)";
          ctx.fill();
        }

        drawLine(ctx, _circle) {
          let dx = this.x - _circle.x;
          let dy = this.y - _circle.y;
          let d = Math.sqrt(dx * dx + dy * dy);
          if (d < 150) {
            ctx.beginPath();
            //开始一条路径，移动到位置 this.x,this.y。创建到达位置 _circle.x,_circle.y 的一条线：
            ctx.moveTo(this.x, this.y); //起始点
            ctx.lineTo(_circle.x, _circle.y); //终点
            ctx.closePath();
            ctx.strokeStyle = "rgba(204, 204, 204, 0.3)";
            ctx.stroke();
          }
        }

        // 圆圈移动
        // 圆圈移动的距离必须在屏幕范围内
        move(w, h) {
          this._mx = this.x < w && this.x > 0 ? this._mx : -this._mx;
          this._my = this.y < h && this.y > 0 ? this._my : -this._my;
          this.x += this._mx / 2;
          this.y += this._my / 2;
        }
      }
      //鼠标点画圆闪烁变动
      class currentCirle extends Circle {
        constructor(x, y) {
          super(x, y);
        }

        drawCircle(ctx) {
          ctx.beginPath();
          //注释内容为鼠标焦点的地方圆圈半径变化
          //this.r = (this.r < 14 && this.r > 1) ? this.r + (Math.random() * 2 - 1) : 2;
          this.r = 8;
          ctx.arc(this.x, this.y, this.r, 0, 360);
          ctx.closePath();
          //ctx.fillStyle = 'rgba(0,0,0,' + (parseInt(Math.random() * 100) / 100) + ')'
          ctx.fillStyle = "rgba(255, 77, 54, 0.6)";
          ctx.fill();
        }
      }
      //更新页面用requestAnimationFrame替代setTimeout
      window.requestAnimationFrame =
        window.requestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.msRequestAnimationFrame;

      let canvas = document.getElementById("canvas");
      let ctx = canvas.getContext("2d");
      let w = (canvas.width = canvas.offsetWidth);
      let h = (canvas.height = canvas.offsetHeight);
      let circles = [];
      let current_circle = new currentCirle(0, 0);

      let draw = function () {
        ctx.clearRect(0, 0, w, h);
        for (let i = 0; i < circles.length; i++) {
          circles[i].move(w, h);
          circles[i].drawCircle(ctx);
          for (j = i + 1; j < circles.length; j++) {
            circles[i].drawLine(ctx, circles[j]);
          }
        }
        if (current_circle.x) {
          current_circle.drawCircle(ctx);
          for (var k = 1; k < circles.length; k++) {
            current_circle.drawLine(ctx, circles[k]);
          }
        }
        requestAnimationFrame(draw);
      };

      let init = function (num) {
        for (var i = 0; i < num; i++) {
          circles.push(new Circle(Math.random() * w, Math.random() * h));
        }
        draw();
      };
      window.addEventListener("load", init(60));
      window.onmousemove = function (e) {
        e = e || window.event;
        current_circle.x = e.clientX;
        current_circle.y = e.clientY;
      };
      window.onmouseout = function () {
        current_circle.x = null;
        current_circle.y = null;
      };
      
    </script>
  </body>
</html>
